1. Field of the Invention
The present invention relates to a vehicle lifting jack for supporting the vehicle body above the ground, and more particularly to a jack of a screw type.
Description of the Prior Art
A conventional screw type vehicle jack generally includes a base and a pantographic mechanism having a lower end pivotably connected with the base and an upper end supporting a head bracket for engagement with the vehicle body. More specifically, the pantographic mechanism includes a pair of lower arms which are pivotably connected with the base at the lower ends and a pair of upper arms connected at the lower ends respectively with the upper ends of the lower arms and carrying a head bracket at the upper ends. The lower and upper arms form a pantographic mechanism so that the vertical distance between the base and the head bracket is changed by adjusting the horizontal distance between the connections of the respective lower and upper arms.
In order to change the distance between the connection of the upper end of one lower arm and the lower end of one upper arm and the connection of the upper end of the other lower arm and the lower end of the other upper arm, there is provided at one of the connections a nut member having internal screw threads. A screw shaft is inserted through the nut member and one end of this shaft is rotatably connected with the other connection. Thus, a rotation of the screw shaft in opposite direction causes one of the connections between the lower and upper arms to horizontally move toward or away from the other connection, and the height of the head bracket is varied in response to this rotation of the screw shaft.
Usually, the head bracket is so designed that it is suitable for engagement with a jack point formed at lower edge portions of the side sill of the vehicle body. In general, the side sill of the vehicle body is formed by welding suitably formed sheet metal parts into a structure of a closed cross section. The side sill parts have welding flanges which extend along the lower portion of the side sill and substantially flat portions of limited width are provided at the opposite sides of the connecting flanges.
According to one form of the conventional structure, the head bracket is designed so that it is engaged at the upper surface with the connecting flanges of the side sill. In another form, the head bracket is formed with a groove for accommodating the connecting flanges so that the head bracket is engaged at the upper surface with the flat portions of the side sill. It should however be noted that in the structure wherein the head bracket is engaged with the connecting flanges of the side sill, the load supporting the vehicle body is concentrated to a very limited portion of the side sill so that the side sill connecting flanges may be easily deformed. In the structure having a groove for accommodating the side sill connecting flanges so that the head bracket can engage the flat portions of the side sill, the supporting load may be distributed to a relatively wide area of the side sill, however, there arises another problem in connection with the manner of storing the jack in the vehicle body.
Usually, the screw type vehicle jack is stored in a trunk of the vehicle body along a side or rear wall or along a floor panel. In storing the jack in this way, the jack is firmly held in position by having the base engaged with a support bracket provided on the wall along which the jack is stored. There is further provided on the wall a second bracket with which the head bracket is engaged at the groove. In this storing position, it is required that the groove in the head bracket is in the direction substantially parallel with the direction of the screw shaft. It should however be noted that in using the jack the direction of the groove must be perpendicular to the direction of the screw shaft. For the reasons described above, the conventional structure of this type is designed so that the head bracket is rotatable about an axis perpendicular to the screw shaft. The structure is however disadvantageous in that the rotatable connection of the head bracket is not strong enough so that this connection may be inadvertently broken in case where the jack is inclined in use.
Japanese utility model publication No. 52-7626 discloses a jack structure having a head bracket formed with a groove for accommodating the connecting flanges of the side sill. In the structure proposed by the utility model, the head bracket is formed integrally with a portion on which the upper arms of the pantographic mechanism are pivotably connected. The structure proposed by the utility model is, however, disadvantageous in that the groove in the head bracket is not engaged with the aforementioned second bracket in the storing position so the jack is not held firmly in the storing position.